I think they'll protect the price cap for energy when the time comes.
They've gone for April because Labour originally said 6 months so they can say "but Labour ...." and also because it will calm the markets for now as it isn't a 2 year spending guarantee.
I can't see how they can think raising it that much will be any good for people and not cause more of a recession when peoples mortgages have risen beyond expectations.
People won't have any money for the economy to grow and businesses won't invest with no energy guarantee.